The invention relates to a cooling apparatus utilizing the Joule-Thomson effect and containing
(a) a lead conduit having an inlet end connectable to a source of pressurized gas, and an outlet end,
(b) a relief nozzle provided at the outlet end of the lead conduit whereby pressurized gas inflowing through the lead conduit, is depressurized with cooling at the relief nozzle,
(c) a return for the cooled and depressurized gas,
(d) a countercurrent heat exchanger by means of which the pressurized gas inflowing through the lead conduit is in heat conductive contact with the cooled and depressurized gas outflowing through the return, and
(e) Peltier elements each having a warm side and a cold side connected to the inlet end of the lead conduit for additional cooling of the inlet end of the lead conduit.
German Published Patent Application No. 3,642,683 describes a cryostat which is based on the Joule-Thomson effect, for cooling an infrared detector. In this cryostat a countercurrent heat exchanger containing a lead conduit is seated in a Dewar vessel. The lead conduit terminates in a relief nozzle. The infrared detector is seated at the end face of the internal wall of the Dewar vessel. A heat insulating layer is disposed intermediate the Dewar vessel and a base for reducing the heat load. For improving the cooling effect achievable by the Joule-Thomson process in a given mass flow of pressurized gas, an inlet end of the lead conduit is cooled by means of Peltier elements.
In the cryostat according to German Published Patent Application No. 3,642,683 the inlet end of the lead conduit is mounted at a carrier made of well heat conducting material and is in good heat conductive contact therewith. The carrier is retained at a heat dissipating base by means of Peltier elements. In this arrangement the cold sides of the Peltier elements are in contact with the carrier and the warm sides of the Peltier elements are in contact with the base.
While it is generally known to cool the warm sides of Peltier elements by heat exchanging means, it has not become known to make use of such construction in combination with Joule-Thomson coolers.
Thus, for axample, a publication by H. Mueller entitled "Design and Set-up of Peltier apparatus" in the Journal "Kaltetechnik" Vol. 15, No. 5, pages 137 to 145, 1963, is concerned with the general construction of Peltier elements. As illustrated therein in FIG. 8, and for similar arrangements in FIGS. 11 and 12, the heat is removed by means of an evaporator; the vaporized liquid is recondensed in a heat exchanger and flows back into the evaporator. A liquefier is seated on the cold side at the Peltier elements. This arrangement does not contain a heat exchanger which is immediately connected with the warm sides of the Peltier elements. Also, there is not present a Joule-Thomson cooler and the warm sides of the Peltier elements are not in heat exchange with the depressurized and cooled gas of the Joule-Thomson cooler. In the FIG. 13 arrangement, cooling of the warm sides of the Peltier elements is effected by cooling water.
A cooling and heating device containing a heat pump is described in U.S. Pat. No. 4,718,249. According to FIG. 1c thereof, a "thermoelectric module" may serve as such heat pump. Also in this arrangement the cold sides and the warm sides of the Peltier elements which constitute the thermoelectric module, are connected to respective circuits through which a heat transfer fluid is circulated and which contain respective heat exchangers.
In an air drier according to U.S. Pat. No. 4,400,948, air is passed through a heat exchanger which is connected with the cold sides of a "thermo-electric module". The warm sides of Peltier elements thereof are cooled using an air stream which is sucked in by means of a ventilator.
In an apparatus according to German Published Patent Application No. 3,541,645, Peltier elements are employed for recovering water from air. The warm sides of the Peltier elements contain heat exchangers exposed to external air, see FIG. 4, part 26.
A cooling box according to European Published Patent Application No. 0,271,704 also operates using Peltier elements. The goods to be cooled are cooled by means of an air stream which is in contact with the cold side of Peltier elements through a heat exchanger. The heat is removed from the warm sides of the Peltier elements by means of a circulating cooling agent which, in turn, transfers heat to the surrounding air by means of a heat exchanger.
While it is known from the aforementioned prior art to remove heat from the warm sides of Peltier elements by using various means for generating forced cooling, such heat removal is not effected in connection with a Joule-Thomson cooler. Also the initially discussed German Published patent application simply teaches contacting the base and the warm sides of the Peltier elements. The aforenoted printed publications thus do not suggest or indicate that the efficiency of the Joule-Thomson cooler is significantly or superproportionately improved by the inventive measures as will be explained further hereinbelow.